Ellipsograph



Oct. 7, 1952 R, FOWLER 2,612,691

ELLIPSOGRAPH Filed Feb. 18, 1952 2 SHEETS-SHEET 1 ',2 llHllulwml. f

.F12-6J. 4. BY

R. L. FOWLER oct. 7, 1952 ELLIPSOGRAPH Filed Feb. 18, 1952 Il \\\\\\\\\n fill. Il

QnLpl-a l.) rowLEl IN VEN TOR.

DTTORNEYS Patented Oct. 7, 1952 UNWD'l STATES PATENT l,oiiucir ELLIPSOGRAPH l Ralph L. Fowier, Whittier, oeuf. 'Application February '18, 1952, serial No. 272,193

Another o-bject ofthe invention is to provide y an ellipsograph which is adjustable so that any size of ellipse from virtually a point to the maximum size vof theinstrument can be easily and accurately drawn. j y

With the foregoing and other objects in view, which will be made manifest in the following detailed description and specifically pointed out in the appended claims, reference is had to the accompanying drawings for an illustrative embodiment of the invention, wherein:

Figure l is a top pla-nview of the ellips-ograph embodying the presentv invention, parts being broken away and shown in horizontal section, the ellipsograph being sho-wn in that position wherein it is being adjusted for the minor axis of the e1- lipse;

Fig. 2 is a view similar to Fig. l, the parts being shown wherein the 'instrumentimay be adjusted for the major axis of the ellipse;

Fig. 3 is a vertical section taken substantially upon the line 3 3 upon Fig. 2;

Fig. 4 is a partial view in" vertical section taken substantially upon the line 4-4 upon Fig. 2;

Fig. 5 is a vertical section taken substantially upon the line 5-5 upon Fig. 3;

Fig. 6 is a partial vertical section taken 'substantially upon the line6-6 upon`=Fig. 3; and

f Fig. '7 is a diagram to illustrate a methern-atical proof of the accuracy of the improved ellipsegraph. ir

Referring to the accompanying drawings wherein similar reference characters designate similar parts throughout, the improved ellipsogra-ph comprises a rectangular base generally indicated at Ihavingop'posed sides II and l2 connected by ends I3 and I4. The opposed faces of the sides II and I2 are grooved as indicated at I5 so as to slidingly receive the side edges of aprectangular slide I6. The ends I3 Iand I4 are disposed above the tops of the grooves I5 as clearly shown in Fig. 3 so'that the ends will not interfere y with the sliding movement of the lslide I6 but will permit the endsv of the slide IS to pass therebeneath if occasion requires. The grooves I5 which slidingly receive the side edges of the slide I6 constitute one guide means on the base I Il. A second guide means on the base is arrangedv at :right angles thereto and is provided by a stationary bridging crosshead Il that extends across the base over the slide I6 and has a groove I3 formed von its underside. Y A

Within the slide I6 two tangentially arranged circular openings are provided indicated at I 9 land,

20. These'openings are preferably iiangedas indicated at 2 I 1,' the flanges serving to slidably support two rotors 22 and 1..'3.v The two rotors 22 and 23 are preferably in the form of equal-sized gears having gear teeth 24 which mesh with eachother at the point of tangency so that when one rotor,

A This adjusting screw is provided with an adjust'- `The arm 34 serves to rotatably support an adjusting screw 3E which is threaded through a nut 31 that is'slidable between spaced guides 38 ar'idf39 provided by the arm. The nut 3'! carries a stylus 4t that extends downwardly through the sloty32 when the arm 34 is in the position shown in Fig. 3. The stylus may be merely a pencil lead, la pen, a steel scribe, or it `may even be a cutter, suche-.s for example an Oxy-acetylene cutting torch.` The hinge connection aiorded by the hinge pin v35 enables the arm 34 to be swung into aposition wherein the stylus, whatever its form may be,'can be adjusted or replaced. Preferably, the arm'34 carries a suitable knob `or handle al by which the rotor 22 can be rotatedA about its center relatively tothe' slide I6. if desiredthe arm 34 lmay be equipped with graduations V42 arranged to be traversed by a palmeras rim the nutsi so martire distance that the stylus is fromvthe center ovffthe rotor 22 'can' be read or 'ascertained therefrom'. In a similar manner, the rotor vZtl'may be equipped with graduations 44 so that the distance that the pin 30 is from the center of the rotor 23 can be ascertained therefrom.

It will be appreciated that motion of the slide I6 relative to the base I0 is limited to linear motion afforded by the guide grooves I5. This linear motion is produced by rotating the rotor 22 by means of the knob 4I relative to the slide I6 which, in turn, causes the rotor 23 to rotate at the same rate fand 1in the opposite direction. Rotation ofthe rotor 23 produces rotation of the pin 30 about the center of the rotor 23 and produces transverse movement of the slide 3l relative to the crosshead I1. When such motion takes place, if the stylus 40 is in contact. with any reasonably iiat surface it will`draw a true ellipse thereon. l f

In order to adjust the ellipsograph to meet dierent conditions the center of the rotor 22 is first positioned over the center of the ellipse to bedrawn with they length of the arm *.34 arranged parallel to. the crosshead Il. To facilitatesuch positioning the slide maybe provided with suitable-marks .indicated at 45 which will assist in sighting the center .of therotor to position it .over theffcenter- `o-f the ellipse. The major partsv of the ellipsograph, including the base ID, the slide I6, and the two rotors, are preferably -formed of a transparentfmaterial, such as a synthetic resin plastic so that the surface on which the ellipse is to be drawn .maybe seen therethrough.

.Y When .thecenter of .the rotor 22 h as been Vposif tioned over the center of ythe -ellipse as illustrated in 1, ythe adjustingscrew 36 is :adjusted so as to vspace the stylus lIll from the center-a distance equal to one-half the length of the minor axis of `the-ellipse. Whenthe .stylus hasY been so adjusted the rotor 22 is .rotated through 90 or into the position shown in Fig. 2, and the-adjusting screw 281s adjusted vso that the stylus 40 overlies one Vlendof thehmajor .axis of the ellipse. When the ellipsograph has been thus adjusted one completerevolution of the Vrotor rv22 will cause the scribing of onefcomplete vaccurate ellipse. The motion imparted to `the stylus is a combination of rotary `and linear .motion produced by the con.- nection between the rotor 23 and the crosshead Ir'I and the guiding of. therslide I6 by thesides Il and, I2 of the base Ill.

Adjustment of the stylus 40 towardthe center of.' the rotor 22 isunlirnited. In other words, the stylus Ill may be positioned at or very close to the center of the rotory 22. In a similar manner,

the center of the .pin 3D may be positioned over or Very close to lthe center of therotor 23. Conf sequently, the improved ellipsograph can be employed to scribe Very. small ellipses and the maximum` size of. the ellipse is limited only by the length ofthe slot 32.

A'Io mathematically prove that the path traversed by the stylus 40 is that of a true ellipse, re'ferenceis made 4to Fig. 7 wherein the periph-A eries of the two rotors22 and 23 are represented by the two full-line circles 50 and 5I which are tangent to each other alongthe X coordinate XTX. These circlesare indicated as being of the .same diameter and rotating at the same speeds but in opposite directions. On the circle 50 which represents the rotor 23 there is a point Q corresponding to the axis of the pin 30, the movement ofv which is restricted to movement along the line Z-Z in the same manner that the pin 30 has its movement restricted by means ofthe, stationarycrosshead I'I. As the circle'SIl .rotates tliepointQ'. in descending to the point 4 Q' along the line Z--Z causes the center O of the circle 50 to shift from O to O' and simultaneously the center of the circle 5I will be caused to shift from its initial center O to O'. The shifted positions of the two circles are indicated by the dotted line circles 52 and 53, respectively. During the shift of the point Q to Q', circle 50 will rotate through an angle 0 and during the shift or rotation of the circle 50 through angle 0 circle '5I will likewise rotate through the same 'angle 0. The point Q' 'is assumed to be at a radius C from the center O' andthe point P' on the circle 53 is assumed at a radius A from its center O'. The problem then is to iind the equation traced by the point P. In proceeding through thepoint P on the curve L, the position of the point P is tovbe determined with respect 'tothe original center O and with respect to the original coordinate Y-Y and X-X. The angle 0 is the parameter. As the rotor 23 is restricted bythe slide `i6 to movement' only along the Xee-X coordinate the Y position of point P `is:

`YED"`O'P' COS 05A 00S i9- Thedistance that point `P moves along the 'X-@X axis while rotatingy through angler 'is:

XEPPleOO OO'EQ' then L=C sin @el-EPv Xie-A 'sin @+C sin r19 X2: sin 'MA-FC) The 'radii C and A are constants and consequently lthe sum of these radii equals a new constant which may be represented by B. Substituting B for the sum C plusA, j

X.=B sin Hand Y=A cos 0 These are parametric equatio-ns of the locus of the path traversed bythe point P to P.

This equation is the equation of a vtrue ellipse. Consequently, regardless of thelength of radius A to the point represented by P which corresponds to the distance that the stylus 40 is from the center of the rotor 22 and regardless of the length of radius C which corresponds to the distance that the pin 30 is from the center of'rotor 23., the point P will be caused to traverse the path of a true ellipse.

From the above-described construction it will be appreciated that an improved ell-ipsograph is provided which is relatively simple in *construction and which `will scribe a true ellipse. The arrangement of parts is such that if the center orf the proposed ellipse is known and the `length of its major and minor axis is also known that theellipsographcan be easily and quickly ad- `justed with respect to these Vknown factors and `then be caused. to scribe a true ellipse. The arrangement is alsosuch that the device canbe used to draw very small ellipses where occasion so requires in that the radial distance of the stylus 40 from the center of its rotor 22 can be very small and likewise the radial distance of the pin 30 from the center of the rotor 23 can be very small. In fact, the instrument can be used to draw ellipses from 0 to 90, that is from a straight line, when the minor axis is of no appreciable length, to a full circle which is the situation when the minor axis and the major axis are equal.

Various changes may be made in the details of construction without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. An ellipsograph comprising a base, a slide slidably mounted thereon for sliding movement in a straight lateral direction, a pair of equal sized tangentially arranged rotors rotatably mounted on the slide having mutually engaged peripheral teeth for causing the rotors to rotate in unison but in opposite directions, a crosshead extending across the base at right angles to the direction of sliding movement of the slide, a slide on the crosshead, means connecting one of the rotors to the slide on the crosshead, a slot in the other rotor, and a stylus mounted on said other rotor extending through the slot.

2. An ellipsograph comprising a base, a slide slidably mounted thereon for sliding movement in a straight lateral direction, a pair of equal sized tangentially arranged rotors rotatably mounted on the slide having mutually engaged peripheral teeth for causing the rotors to rotate in unison but in opposite directions, a crosshead extending across the base at right angles to the direction of sliding movement of the slide. a slide on the crosshead, means connecting one of the rotors to the slide on the crosshead, a slot in the other rotor, and a stylus mounted on said other rotor extending through the slot, the connecting means between said one of the rotors and the slide on the crosshead being adjustable as to length to vary the distance between the slide on the crosshead and the center of said one of the rotors,

and the mounting means for the stylus on said f other rotor being adjustable so as to radially vary the position of the stylus from the center of said other rotor.

3. A n ellipsograph comprising a base, a slide slidably mounted thereon for sliding movement in a lateral direction, there being a pair of y tangentially arranged openings in the slide, rotors rotatably mounted in said openings, said rotors being of equal size and having peripheral teeth in mutual engagement causing the rotors to rotate in unison but in opposite directions, a crosshead extending across the base at right angles to the direction of sliding movement of the slide, a slide on the crosshead, means connecting one of the .rotors to the slide on the crosshead to vary the position of the center of the mentioned rotor with respect to the slide on the crosshead, a radial slot in the other rotor, and a stylus adjustably mounted on said other rotor for radial adjustment with respect to said other rotor and exf tending through the slot.

RALPH L. FOWLER.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,876,069 OByrne Sept. 6, 1932 2,595,417 Scott May 6, 1952 FOREIGN PATENTS Number Country Date 360,248 Germany Sept. 30, 1922 "r'f--LI-"rrr- 

